The present invention relates to a clamp collar of the annular band type provided with connecting means for connecting at least one pair of adjacent ends of the band, and to a run-flat device intended to be fitted to a motor vehicle mounted assembly incorporating same.This clamp collar (40) comprises a band (41), preferably made of metal, having at least one pair of ends (42 and 43) spaced apart in the circumferential direction, connecting means (44) of connecting the or each pair of ends together with adjustable tightening in this direction and a locking member (45) for locking the connecting means.According to the invention, this member is mounted solid with one of these ends (43) being able to occupy an unlocked position in which it is disengaged from these means for tightening and loosening the collar and a locked position in which it engages with them to oppose this loosening.